The present invention relates generally to production machinery used in the manufacture of color cathode ray picture tubes, and is particularly directed to apparatus and method for inserting a shadow mask into the face panel.
The shadow mask is of the type disclosed in U.S. Pat. No. 4,100,451 to Palac, of common ownership herewith. The face panel into which the shadow mask is to be inserted is substantially rectangular and supports on a concave inner surface thereof in a central region a phosphor screen comprising patterns of red-, blue-, and green- emissive phosphor compounds deposited in stripe form and grouped into triads comprising the three colors. The low-mass, approximately rectangular shadow mask has a central portion with a pattern of electron-transmissive apertures in registry with associated ones of the triads. The mask has a skirt portion providing substantial rigidity with respect to axes normal to the side thereof, while providing for flexure of the mask with respect to its diagonals. The suspension system for the mask establishes a predetermined position of the mask relative to, and at a predetermined spacing from, the inner surface of the face panel. The system includes four suspension means for mechanically coupling the mask directly to the corner portions of the face panel. The suspension means are located at each corner of the mask to permit the mask to flex about its diagonals and conform to the contour of the face panel despite any twist-wise deformation thereof. By this means, the predetermined spacing between the mask and the face panel inner surface is maintained.
FIG. 1 depicts in detail the aforedescribed mask-face panel assembly 10 which comprises a substantially rectangular, frameless, shadow mask 12 having a dished perforate central section 14 and a rearwardly extending skirt 16. Mask 12 has an integral rim 18 extending radially outwardly from the rear edge of the mask skirt 16; integral rim 18 serves as an electron beam shield and provides added stiffness to mask 12. Mask 12 is relatively stiff about its major axis 20 and minor axis 22, but torsionally flexible and unstable with respect to diagonals 24 and 26. Shadow mask 12 is shown as cut away in FIG. 1 to reveal a glass face panel 28 having a dished central section 30. Face panel 28 has a rearwardly extending flange 32. Enlarged area 31 depicts the pattern of apertures in mask 12, ones of which are in registry with associated ones of the phosphor stripes deposited on face panel 28, indicated by enlarged area 33.
A corner mask suspension system for rigidly and stably suspending mask 12 from the dished central section 30 of face panel 28 is shown as comprising four suspension devices 34. One such device is located at each corner of the mask 12 to provide four-corner mounting. In consequence of the four-corner mounting system, the mask, which is low in cost but inherently lacking in self-rigidity due to its one-piece, frameless construction, is suspended with high rigidity derived from flange 32 of face panel 28, and high stability derived from the four-corner, diagonal mounting.
With additional reference to FIG. 2, there is shown in detail a corner mask suspension device 34 and associated components. A lip 36 may extend downwardly from rim 18 of mask 12 to add stiffness to mask 12. A stud 38 is shown as being affixed to the face panel flange 32 on the associated face panel diagonal 26. Stud 38 is arranged to extend radially inwardly along diagonal 26, as indicated.
An outwardly biased leaf spring 40 provides for detachably interconnecting the corner of mask 12 to stud 38 on the rearwardly extending flange 32 of face panel 28. Spring 40 has an aperture 41 at its distal end 42 for detachably interconnecting the mask corner to the face panel flange 32 by engagement of aperture 41 with stud 38. Spring 40 is depicted as being attached to bracket 43, which in turn is shown as being attached to skirt 16 of mask 12. It will be observed that when spring 40 is deflected, its distal end 42 will travel on an arc inwardly toward the face panel central axis, as indicated by arrow 44. Rearwardly extending leaf spring 40 will be seen to have its distal end 42 readily accessible for facile insertion and removal of mask 12 from face panel 28.
This corner mask-suspension system if fully described and claimed in referent copending application Ser. No. 101,959. Leaf spring 40 is depicted in FIG. 2 as having a radially extending lip 45 at its distal end 42.
The well-known process of successive application of the color phosphors and other screening fluids to the inner surface of the face panel requires that the shadow mask be removed and inserted in proper registration several times during production. Upon each re-insertion, the shadow mask must re-assume its precise proximate position with respect to the associated face panel; the required tolerance in directions perpendicular to the axis of the cathode ray tube is .+-.0.0004 inch. Any mispositioning of the shadow mask beyond this limit from its predetermined precise location will result in misregistry of the electron beams that excite the phosphors. The result of such misregistry can be color impurities, white non-uniformities, and other deleterious effects that degrade color television picture quality.
Although the shadow mask can be inserted into and removed from the face panel manually, it is far more efficient to perform the operation by an automatic apparatus. By its nature, such an apparatus is quicker, more positive in operation, and is less likely to damage the face panel and/or the mask in the mask insertion and removal operation. Also, foreign matter such as airborne dust and human hair is less likely to fall onto the mask or phosphor screen as the panel is handled open-side-down by the apparatus. The presence of such foreign matter in active areas of the face panel assembly can result in rejection of the cathode ray tube of which the assembly is a part.
The major constraint in the design of shadow mask inserters lies in the unpredictable variance in dimensions of face panels which may exhibit deviations of as much as .+-.0.075 inch. Additional deviations of as much as 0.050 inch may exist in the shadow mask. These deviations relate to variations in the length of springs, spring curvature, aperture dimensions and point of attachment with respect to the shadow mask. It is to be noted that the dimensional deviations set forth--0.075 inch for the face panel and 0.050 inch for the mask--can be additive, and the totality must be taken into consideration in the design of automatic apparatus. If the tolerances are not taken into consideration, a condition may occur wherein one or more of the spring apertures may entirely escape engagement with the associated studs.
Representative apparatus for automatic insertion of shadow masks is disclosed by the following U.S. Pat. Nos:
Baranski et al--3,889,812 PA1 Oyama--4,188,695 PA1 Hartta--4,164,060.
These disclosures are directed to the insertion of shadow masks wherein the suspension springs are parallel with a mask frame on which they are mounted.